The invention concerns transfer foils for applying a decorative layer arrangement formed by at least one lacquer layer and a heat-activatable adhesive layer to a substrate.
Safeguarding documents is becoming increasingly important, in which respect the term xe2x80x9cdocumentsxe2x80x9d is used to mean not only identity papers, value-bearing papers or stocks and shares or the like but for example also banknotes, cheques, credit cards etc. Value-bearing documents, for example banknotes, very frequently involve using security elements formed by a decorative layer arrangement which for example includes structures having an optical-diffraction or holographic effect. In addition however it is also possible to provide given graphic configurations as security elements. In the case of value-bearing documents issued in large numbers the security elements are very frequently applied by means of a transfer foil, for example a hot stamping foil, in which case the decorative layer arrangement forming the security element usually includes at least one lacquer layer and a layer of a heat-activatable adhesive which serves to join the lacquer layer or assembly of lacquer layers which represent the actual security element, to the substrate, for example a banknote, a cheque, an identity document or a credit card.
In most cases the operation of transferring the security element onto the document is effected by machine. In that situation processing of transfer foils, mostly so-called hot stamping foils, gives rise to few problems if the machines are of a suitable design.
The decorative layer arrangements of hot stamping foils are only of very small thickness. They comprise essentially only some lacquer layers. The advantage of this small thickness of the security elements is that, when the security elements are arranged only in a given region of the document, there are nonetheless no fundamental differences in thickness in the document. Such differences in thickness could in fact give rise to problems in regard to the stacking operation. A further advantage of using decorative layer arrangements comprising a plurality of lacquer layers as security elements is that layer arrangements of that kind are mechanically not very stable. If therefore the attempt is made to pull a security element off the document, it is virtually safe to assume that the security element comprising the various lacquer layers will be destroyed so that the forgery or the attempt at forgery can be easily detected.
The use of hot stamping foils for applying security elements to documents does however suffer from the disadvantage that it is always necessary to incur a corresponding amount of machine expenditure because applying hot stamping foil decorative layers as security elements to substrates by hand is practically impossible, more specifically because of the very small thickness of the decorative layer arrangement of a hot stamping foil. This means that for specific situations of use, the use of hot stamping foils as a security element was hitherto out of the question because the machine expenditure required would not have been in reasonable relationship with the result attained.
In certain cases it would moreover be highly advantageous if a security element could be individualised before being applied to a document. That option is worthwhile in particular in relation to personal documents. It would then be possible to use a security element which, before being applied to the document, was individualised with personal data of the owner of the document, for example a photograph, name or date of birth etc. That possibility is out of the question in a practical context if security elements are transferred onto a document by means of a known hot stamping foil, more specifically in particular for the reason that individually printing security elements which are always present in very large numbers on hot stamping foils is once again out of the question, because of the expense involved, if only a few, correspondingly individualised security elements are required. By way of example the situation is such that only very few security elements with person-related data are always required for personal identifications, passports etc. Frequently even one such element is sufficient, which is then a component part of the personal identification or passport.
Now, the object of the invention is to provide a transfer foil by means of which it is possible to transfer a security or decorative element which in terms of its structure basically corresponds to the decorative layer arrangement of a per se known hot stamping foil, wherein application of the decorative layer arrangement to the substrate, for example a document, is to be possible, even without extensive machine equipment.
In accordance with the invention, to attain that object, there is proposed a transfer foil of the kind set forth in the opening part of this specification, which includes a base foil which is connected by means of a permanent adhesive to the one surface of a carrier film, at the other surface of which is arranged the decorative layer arrangement which is releasable from the carrier film under the effect of heat, and which on its side remote from the carrier film has the heat-activatable adhesive layer serving for joining to the substrate.
The transfer foil according to the invention therefore differs from per se known hot stamping foils in that, in addition to the carrier or backing film which is provided in known hot stamping foils for stabilisation of the decorative layer arrangement, there is an additional base foil which is joined to the carrier film by means of a permanent adhesive. In that respect the carrier film and the base film are usually joined after manufacture of the actual hot stamping foil. In accordance with the invention therefore there is afforded a transfer foil which is of comparatively, high stability because, instead of the relatively thin carrier film which is hitherto usual in the case of hot stamping foils, there is a combination of base foil and carrier film which enjoys the necessary stability so that the transfer foil can be handled neatly and tidily even without expensive machines. In use, the user lays a transfer foil of that kind with the side on which there is the decorative layer arrangement with the adhesive on the substrate. Then, by the appropriate action of pressure and heat, the decorative layer arrangement is joined to the substrate and then the carrier film jointly with the base foil is pulled off the decorative layer arrangement which remains behind on the substrate. Thus, when using the transfer foil in accordance with the invention, there is the possibility of transferring a very thin decorative layer arrangement which hitherto could only be applied by means of the hot stamping foil procedure to the substrate, for example a document. At the same time however handling of the transfer foil is greatly simplified by virtue of the stability of the combination of base foil and carrier film. In the case of the transfer foil according to the invention the decorative layer arrangement can be designed in the manner which is known from hot stamping foils. In particular there is no need to provide for corresponding stability of the decorative layer arrangement in itself because that decorative layer arrangement is sufficiently stabilised during manufacture by virtue of the presence of the carrier film.
In accordance with the invention therefore there is proposed a transfer foil which, in comparison with known hot stamping foils, enjoys a substantially wider area of use, and which in particular can be securely and reliably processed even by means of very simple apparatuses. Nonetheless the transfer foil in accordance with the invention, in regard to the decorative layer arrangement, enjoys all design configuration options known hitherto from hot stamping foils.
It has proven to be advantageous if the base foil is formed by a paper web which is siliconised on its surface remote from the carrier film and which detachably adheres with its siliconised surface to a carrier foil, for example a carrier paper. In that case for example a plurality of small security elements can be arranged on a common sheet, namely the carrier foil. For use in that respect, a security element comprising the base foil, carrier film and decorative layer arrangement is then released from the carrier foil and suitably transferred onto the intended substrate.
That operation of transferring individual elements can advantageously be made easier if the base foil with the carrier film and the decorative layer arrangement is subdivided into a plurality of label-like individual elements, wherein a plurality of such individual elements are arranged on a carrier foil web in such a way they can be pulled therefrom. In that respect the subdivision is desirably such that the individual elements are formed by stamping or perforating the base foil, the carrier film and the decorative layer arrangement along their intended peripheral edges, without the carrier foil being cut.
A particularly advantageous embodiment of the transfer foil according to the invention is designed in such a way that the decorative layer arrangement is transparent and the adhesive layer which serves for fixing the decorative layer arrangement to the substrate can be applied by printing by means of a printer, for example a laser printer or a thermal printer. In the case of a transfer foil of that kind, suitable individualisation can be effected for example by the operation of printing on the adhesive layer. It is for example possible for the side of a passport which contains the personal data to be safeguarded by using a transfer foil in accordance with the invention, in which case the basic information can already be applied upon manufacture of the transfer foil in the factory, in a suitable printing operation, for example between individual layers, which involve the entire surface area, of the decorative layer arrangement, while the person-related data, for example surname, forename, address, dates of birth and picture of the holder are then applied by printing before use of the transfer foil on the adhesive layer thereof by means of a suitable printer. After the individualising printing operation the transfer foil is then laid with the printed adhesive layer onto the substrate and fixed to the substrate by heat and possibly the action of pressure. This embodiment enjoys the advantage that the individualising details are concealed by the decorative layer arrangement of the transfer foil, in other words, a modification is not possible without at the same time damaging the decorative layer arrangement. If the attempt is made to pull the decorative layer arrangement off the substrate in order to alter the individualising data, it must be reckoned that the decorative layer arrangement will be destroyed. In addition in a normal situation it is to be assumed that the individualising data are also to be found on the substrate again because, with the usual processing conditions in regard to the transfer foil according to the invention, at least a certain proportion of the printing ink present on the adhesive layer is also directly joined to the substrate.
A further improvement in the transfer foil according to the invention in the sense of affording a safeguard is possible in accordance with the invention by virtue of the fact that the decorative layer arrangement has at least one replication lacquer layer provided at a surface with a structure having an optical-diffraction and/or holographic action. Structures of that kind with an optical-diffraction or holographic action are generally known per se from security elements formed by hot stamping foil decorative layer arrangements and for that reason do not have to be described in greater detail.
In regard to the previous security elements it is now frequently the case that the structure having an optical-diffraction or holographic action is covered by means of a reflective layer, generally a vapour-deposited metal layer, and is thereby better visible under incident light. In accordance with the invention it is preferred if the structure having the optical-diffraction and/or holographic action carries a transparent layer of a material whose refractive index is markedly higher than that of the transparent replication lacquer layer. With such a design configuration, that affords adequate visibility for the optically operative structure. At the same time however the decorative layer arrangement remains transparent so that it is still possible to perceive the substrate and any identifications possibly provided between the substrate and the decorative layer arrangement, for example, printing on the adhesive layer of the decorative layer arrangement. Preferably the material layer which enhances the visibility of the optically operative structure is produced by a layer of ZnS, TiO2, SiO or a material having a similar action in terms of refraction being provided, for example by vapour deposition.
It is further provided in accordance with the invention that the heat-activatable adhesive layer serving for fixing to the substrate is formed by two adhesive layer portions, between which is arranged a marking produced in a printing process, wherein the marking can advantageously be formed by printing inks which are perceivable only upon illumination with light in predetermined wavelength ranges. When in this respect reference is made to two xe2x80x9cadhesive layer portionsxe2x80x9d, it is certainly not necessary for the two adhesive layer portions to be of the same composition and structure. On the contrary, consideration is given in particular to the situation where the first adhesive layer portionxe2x80x94as seen from the carrier filmxe2x80x94is a bonding layer which provides that bonding to the vapour deposited layer which improves the visibility of the diffractive structure is particularly good. It would certainly also be possible to envisage the situation where there is only one adhesive layer, in which case then the marking produced in the printing process would have to be present directly on the layer which improves the visibility of the structure.
In accordance with the demands of the user, the sequence of layers of the decorative layer arrangement will be varied, in which respect usually firstly a hot stamping foil is produced with appropriate layers, and that hot stamping foil is then applied by lamination to the base foil. It will be appreciated that in this case, to join the carrier film of the hot stamping foil to the base foil, it is necessary to use an adhesive which, at the temperatures which are employed for applying the decorative layer arrangement to the substrate, does not suffer a reduction in its adhesive strength and which ensures that the base foil and the carrier film are securely held together.
A particularly advantageous embodiment of the transfer foil according to the invention is distinguished in that it includes the following mutually adjoining constituents or layers:
a carrier paper web,
a web of silicone paper which releasably adheres with its siliconised surface to the carrier paper web,
a carrier film which is joined by means of a permanent adhesive to the non-siliconised surface of the silicone paper web, wherein on its free surface the carrier film has in succession the following layers:
a release layer which is present only if required,
a transparent replication lacquer layer which at its surface remote from the carrier film has the structure with the optical-diffraction and/or holographic action,
a layer which covers the structure at least in a region-wise manner, that layer being of a material with high refractive index in comparison with the replication lacquer layer,
a heat-activatable adhesive layer, and
possibly a second heat-activatable adhesive layer and a printed marking between the two heat-activatable adhesive layers, wherein
the replication lacquer layer, the layer of material with a high refractive index and the heat-activatable adhesive layer or layers are transparent and the adhesive layer forming the surface of the transfer foil which is remote from the carrier foil web is formed by a material which can be printed by means of a printer.
The transfer foil of the configuration described hereinbefore satisfies the demands stated in the opening part of this specification in an excellent fashion. It affords the possibility of applying a comparatively thin decorative layer arrangement which hitherto could be transferred only by means of a hot stamping foil, onto a substrate, without involving a high level of machine expenditure. At the same time the transfer foil according to the invention can be easily handled and it is readily possible to individualisingly print various security elements formed by means of a transfer foil according to the invention.